Aqueous metal iodide solution for use as an x-ray contrast agent



Unite S ates, P l M 3 316 407 AQUEQUS METAL ronmn soLUTIoN FOR USE AS ANX-RAY CONTRAST AGENT -Wataru Ichikawa, Yokohama, Japan, assignor toAsahi Glass Co., Ltd, Tokyo, Japan, a corporation of Japan 5 N0 Drawing.Filed Sept. 30, 1963, Ser. No. 312,299

Claims priority, application Japan, Nov. 2, 1962, 37/49,.282 12 Claims.(Cl. 250-108) The present invention relates to a method of and maskingagents for non-destructive tests, and more particularly to .a method ofand masking agents for non-destructive tests using penetrating radiationor radioactive rays such as X-rays, gamma rays, and masking agents forsuch non-destructive tests.

In recent years, with development of industries, nondestructive tests byradioactive rays have come to play an important role in testing metallicmaterials for detection of interior defects or flaws of castings and andinspection of defects in welded parts. When, however, such methods areapplied to material of complicated configuration havingvarious'unevennesses or bends, fogs of film occur due to the scatteredradiation, and as a result, the image obtained frequently becomesunclear and vague, particularly at the edges of the material tested. Inthis case, however, the image may be improved by taking a photographunder controlled test conditions, for instance, at a low electriccurrent by using a high voltage X-ray tube and low sensitive film.However, this method is accompanied by the disadvantage that theresolving power is lowered. Thus, in the testing of various shapedmaterials having parts of different thicknesses, attempts have beenproposed to take a photograph by applying lead plate to the thinnerparts or using a mold made of low fusible alloy containing heavy metalsuch as bismuth and shaped in conformity with the specimen. It is,however, impossible to apply such a method to material of complicatedconfiguration as it is difiicult to carry out. It has also been proposedto irradiate the material to be tested with radioactive rays, whileimmersed in a liquid-mask composed of an aqueous solution of leadacetate and lead nitrate, or while coated with a paste of bariumsulfate. Such methods are generally insufficient to mask the radiationor radioactive rays. At present, accordingly, only unsatisfactory andunclear images are obtainable with non-destructive tests usingradioactive rays, except with specimens of simple shape.

An object of the present invention is to provide a sharp image excellentin contrast of the edge portions of the material tested, especially whentesting materials of complicated configuration, in a method ofnon-destructive testing using penetrating radioactive rays.

Another object of the present invention in to provide a new liquid-maskfor radioactive rays suitable for use in a method of non-destructivetesting, using the penetrating radiation.

These and other objects of this invention are accomplished by using anaqueous masking solution of an iodide or iodides selected from thecompounds of the folout the non-destructive tests,

lowing group, in carrying using penetrating radiation:

In the hitherto known liquid-mask containing lead acetate and leadnitrate, the solubility of both salts in water is low and generally inthe orderof 50. grams/100 grams H O at 15 C. Consequently, in the casewhere a solution of high concentration is needed as in the test of ironmaterial, the solubility has to be increased by raising the temperature.Therefore, obstacles due to acidity of solution as well as obstaclesaccompanied by acetic acid vapor and nitric acid vapor have beeninevitable. However, in the aforesaid iodide or iodides according to thepresent invention, the solubility in Water amounts to approximately 100to 200 grams/100 grams H 0 01' thereabove even at room temperatures.Moreover, in the case of lead acetate and lead nitrate as the aceticacid radical or nitric acid radical which is over one-thirds by weightof lead acetate or lead nitrate does not display any masking action onradioactive rays, whereas in the iodide or iodides of the presentinvention, there is provided an advantage that the iodine occupying themajor part of the above-mentioned iodide demonstrates not only a maskingpower substantially comparable to that of copper, but the remainingmetallic atoms also have effective masking action on radioactive rays.The iodide and iodides are dissolved in water as such or in the form ofcomplex ions. However, the form of their dissolution has no relationwith the characteristics of the present invention. Inasmuch as theiodide is dissolved uniformly in solution, alcohol, ether and ketone maybe added to the solution.

Materials capable of being tested according to the present invention aremetallic material such as iron, aluminum, copper, brass and the like aswell as ceramic material of high density such as fused refractorymaterial and the like. The kind and concentration of the solutions areselected, depending on the kind of material to be tested as well asconditions of the test. Satisfactory results are obtained when asolution having masking action corresponding to above 30%, preferablyabout 50% of the masking action for radioactive rays of the material tobe tested is used. For testing of iron materials, for

instance, a 50 to by weight aqueous iodide solution is used, and fortesting of aluminum material and fused refractory material, forinstance, an approximately 20% by weight aqueous iodide solution isused.

The aqueous solution containing the iodide or iodides according to thepresent invention may liberate iodine in the course of its manufactureand during its storage. Inasmuch as the iodine thus liberated does notevaporate in air and is dissolved in the solution, the masking actionfor radioactive rays is not affected thereby. However, the strongcoloring or turbidity produced in the solution is not only unfavorable,but also the possibility of the test material being corroded will beincreased. Therefore, it is preferable to add a reducing agent andalkali to the solution.

For example, hydroxylamine and thiosulfate are specified as a suitablereducing agent. The amount of reducing agent to be added is notconstant, but varies in accordance with the amount of free iodinecontained as impurity in the raw material as well as with an amount ofreducing impurities such as ferrous salt and the like. When an iodidecontaining a large amount of liberated iodine is used, powder, bar orfoil of metallic zinc is added thereto at the time the liquid mask isproduced, or the amount of the aforesaid reducing agent is increased.When the content of reducing impurities is high, the amount of reducingagent to be added is decreased. The amount of reducing agent finallyexistent in the solution preferably is such that the Index of Reductantas hereinafter defined is 5 to 100. A large excess of reducing agent isliable to cause precipitation. Furthermore, when thiosulfate is usedalone in a large amount, precipitation occurs sometimes, andconsequently, thiosulfate is used preferably in combination withhydroxylamine.

3 DEFINITION OF INDEX OF REDUCTANT DEFINITION OF INDEX OF ALKALINITY 5cc. of an aqueous iodide solution are mixed with 100 cc. of water andthe mixture titrated with a N aqueous HCl solution. The number of cc. ofthe N aqueous HCl solution consumed until the indicator, methyl redturns red, is defined as the index of alkalinity.

When the index of alkalinity is too high, precipitation of zinc orcadmium hydroxide will occur. Conversely, when the index of alkalinityis below the necessary amount, the solution will be subject to oxidationdue to air, and also the material to be tested is liable to be corroded.Oxides or hydroxides of alkali metals, such as caustic potash or causticsoda, or their aqueous solutions are used as alkali.

The iodide solution prepared as above will not show any changes in itsappearance even when exposed to the atmosphere for at least days.However, if such iodide solution is left to stand for an extended periodof time, the index of reductant and index of alkalinity will decrease,and thus, iodide deposition takes place or finally precipitation occurs.However, such a solution may be used after the precipitate is removed.It is appropriate to reuse the solution after adding the reducing agentand alkali thereto. When iodides of alkaline earth metals are used incombination with zinc or cadmium iodides, there is the tendency toprecipitate carbonate by absorb ing carbonic acid gas from atmosphericair. The formation of carbonate has been ascertained not to impart anyappreciable effect to the measured result in the nondestructive test.Generally, however, it is rather preferable not to use alkaline earthmetals, in order to avoid such occurrence of the precipitation.

Materials to be tested, such as iron, steel, copper, tin or their alloyswill almost not be corroded, even after at least 20 days immersion inthe aqueous iodide solutions according to the invention. Only somediscoloration occurs at a gas-liquid contact portion after an extendedperiod of time. In some cases, it is effective to apply a grease or thelike to material to protect it from corrosion. Particularly when thematerial to be tested is subject to corrosion, it is appropriate toprovide a corrosion-resisting coating around the said material. Forinstance, the material is immersed in a butyl acetate solution ofpolyvinylbutyral and withdrawn after a suitable period of time, to forma corrosion-resisting synthetic resin coating on its surface. Thiscoating may be readily removed after the test. Furthermore, in order toimprove the foaming characteristics at the time when material to betested is immersed in a solution, a defoaming agent, such as surfaceactive agent or the like may be added.

In practicing the method of non-destructive testing using theliquid-mask according to the present invention, the aforementionedaqueous iodide solution is put in a suitable receptacle or vesselpermeable to the penetrating radiation or the radioactive rays, and thewhole or a part of the material to be tested is immersed in the solutioncontained in said receptacle. Then, the test may be conducted byirradiating the test material in the solution with the radioactive raysby a known method. In the case where the material to be tested cannot beimmersed in a solution, the solution is sealed in a deformable bag-likereceptacle made of a sheet of polyethylene, vulcanized rubber and thelike, and then the receptacle is applied against the material to betested and irradiated with radioactive rays. As means for detecting theradioactive rays or penetrating radiation, any of the known means, suchas, photography using a light-sensitive film, or fluoroscopicobservation is suitably adapted. Furthermore, when the deformablebag-like receptacle is to be filled with a solution, it is preferable toadd a soluble starch, gelatine and agar-agar thereto, in order to lowerthe fluidity of the solution. Any suitable permeable radiation orradioactive rays which are generally usable for such a purpose, such as,X-rays and gamma rays can be used as a source of radiation for thenon-destructive tests according to the invention.

Thus, according to the present invention, scattered radioactive rayshaving a deleterious effect upon the film are masked and the wholesurroundings including the materials to be tested can be also subjectedto penetrating radiation or radioactive rays under substantially uniformconditions. Therefore, regardless of the configurations and propertiesof the material to be tested, a sharp image excellent in contrast of theedge portions can be obtained. Moreover, even when the photography iseffected under conditions generally liable to cause fog, a cleardistinct image may be readily and surely obtained.

This invention is further described in the following examples which areillustrative and not limitative thereof.

Example 1 450 grams of zinc iodide and 350 grams of potassium iodidewere dissolved in 200 grams of water, and then 10 grams of hydroxylaminehydrochloride were added to the solution. Thereafter, a caustic potashsolution was gradually dropped into the mixture while the index ofalkalinity was detected. The light yellowish solution thus obtained hada specific gravity of 2.52, an index of alkalinity of 20, and an indexof reductant of 45. At various X-ray tube voltages (kv.p.=kilovoltagepeak), the iron equivalent of the aqueous solution of under-mentionedrespective thicknesses (mm.) [which means thickness (mm.) of ironshowing the same masking power for radioactive rays as that of thesolution] was measured, the results being as follows:

Tube voltage Thickness of liquid:

In the next place, an iron material to be tested of 20 mm. in thicknessand having a sectional form of a rectangular piece 15 x 50 mm. securedat a side of its bottom to another rectangular piece 5 x 40 mm. inL-shape was immersed in this solution, and a photograph was taken byexposing to X-rays at 4 ma. for 1.5 minutes in the vertical direction tosaid section by using X-ray tube of 250 kvp. Then, an image of clearconfiguration and excellent in contrast was obtained.

When the same test material was photographed in air without immersinginto said solution, the image in the narrower portion was entirelyunclear because of fog. Even when various different X-ray tubes wereused or conditions of exposure were changed, no clear image could beobtained.

Example 2 1900 grams of zinc iodide were dissolved in 630 grams ofwater, and 1 gram of hydroxylamine hydrochloride and 0.2 gram of sodiumthiosulfate admixed with the resulting solution. Then, he index ofalkalinity was adjusted to 20 by gradually dropping in a 5% causticpotash solution. The thus-obtained colorless semi-transparent solutionof specific gravity 2.4 had an index of reductant of 11. 'Ifhe ironequivalents of the solution measured in the same manner as in Example 1were as follows:

Tube voltage When this solution was used to that used in Example 1 wassame condition, a clear image and a specimen similar photographed underthe was obtained.

Example 3 grams of grams of Tube voltage mun-m comoomq When thissolution was used and a photograph was taken of a specimen similar tothat used in Example 1, under similar conditions, a clear image wasobtained.

Example 4 180 grams of soluble starch (Japanese trademark: Miraclin)were added to 500 cc. of a 75% by weight zinc iodide solution obtainedas in Example 1 (sp. gravity, 2.4; index of alkalinity, 20 and index ofreductant, 11) and dissolved therein while heating. The thusobtainedsolution having fluidity but of remarkably high viscosity was filled ina polyethylene bag of 0.1 mm. thickness, de-aerated under reducedpressure and immediately thereafter its mouth was sealed. This bag wascaused to adhere firmly to hollow portions and surroundings of thematerial to be tested, so as to become uniform in thickness. Then, thephotograph was taken by irradiating the material to be tested withradioactive rays, and a clear image was obtained.

What is claimed is:

1. In carrying out a nondestructive test by irradiating a material to betested with penetrating radiation; the step of masking the material tobe tested by an aqueous metal iodide solution having masking power forthe penetrating radiation approximately similar to that of said materialto be tested during the irradiation, the aqueous metal iodide solutionbeing selected from the group consisting of aqueous solutions of:

(a) zinc iodide,

(b) cadmium iodide,

(c) iodides of zinc and alkali metal,

(d) iodides of zinc and alkaline earth metal,

(e) iodides of cadmium and alkali metal, and

(f) iodides of cadmium and alkaline earth metal.

2. In carrying out a non-destructive test by irradiating a material-tobe tested with penetrating radiation; the steps of immersing thematerial to be tested in an aqueous metal iodide solution having maskingpower for the penetrating radiation approximately similar to that ofsaid material to be tested during the irradiation, the aqueous metaliodide solution being selected from the group consisting of aqueoussolutions of:

(a) zinc iodide,

(b) cadmium iodide,

(c) iodides of zinc and alkali metal,

(d) iodides of zinc and alkaline earth metal,

(e) iodides of cadmium and alkali metal, and

(f) iodides of cadmium and alkaline earth metal.

3. In carrying out a non-destructive test by irradiating a material tobe tested with penetrating radiation; the steps of masking the materialto be tested by a deformable bag-like receptacle containing an aqueousmetal iodide solution having masking power for the penetrating radiationapproximately similar .to that of the material to be tested, the metaliodide being selected from the group consisting of aqueous solutions of:

(a) zinc iodide,

(b) cadmium iodide,

(c) iodides of zinc and alkali metal,

((1) iodides of zinc and alkaline earth metal,

(e) iodides of cadmium and alkali metal, and

(f) iodides of cadmium and alkaline earth metal.

4. In carrying out a non-destructive test by irradiating a material tobe tested with penetrating radiation; the step of masking the materialto be tested by an aqueous zinc iodide solution having masking power forthe penetrating radiation approximately similar to that of the saidmaterial during the irradiation.

5. In carrying out a non-destructive test by irradiating a material tobe tested with penetrating radiation; the step of masking the materialto be tested by an aqueous solution of zinc iodide and alkali metaliodide having masking power for the penetrating radiation similar tothat of the said material during the irradiation.

6. A method of a non-destructive test as set forth in claim 1, whereinthe aqueous iodide solution contains a reducing agent and alkali.

'7. A liquid-mask for a non-destructive test, comprising an aqueousmetal iodide solution selected from the group consisting of aqueoussolutions of:

(a) zinc iodide,

(b) cadmium iodide,

(c) iodides of zinc and alkali metal,

(d) iodides of zinc and alkaline earth metal,

(e) iodides of cadmium and alkali metal, and

(f) iodides of cadmium and alkaline earth metal, said aqueous metaliodide solution also comprising an alkali and a reducing agent dissolvedtherein.

8. A liquid-mask for a non-destructive test, comprising an aqueous metaliodide solution selected from the group consisting of aqueous solutionsof:

(a) zinc iodide,

(b) cadmium iodide,

(c) iodides of zinc and alkali metal,

(d) iodides of zinc and alkaline earth metal,

(e) iodides of cadmium and alkali metal, and

(f) iodides of cadmium and alkaline earth metal, said aqueous metaliodide solution also comprising thiosulfate, hydroxylamine and alkalidissolved therein.

9. A liquid-mask as set forth in claim 7 having the index of reduc-tantof 5 to 100, as defined in the specification.

10. A liquid-mask for a non-destructive test, as set forth in claim 7having the index of alkalinity of 2 to 25, as defined in thespecification.

11. A liquid mask for a non-destructive test comprising an aqueoussolution of zinc iodide, thiosulfate, hydroxylamine and alkali.

7 11-2. A liquid mask for a non-destructive test comprising an aqueoussolution of zinc iodide, alkali metal iodide, thiosulfate, hydroxylamineand alkali.

References Cited by the Examiner UNITED STATES PATENTS 1,950,543 3/1934Dahru 250-108 OTHER REFERENCES Cl-ar-k: Applied X-rays, fourth edition,McGraw-Hill Book Co., Inc., New York, 1955, pp. 213 and 214.

5 ARCHIE R. BORCHELT, Primary Examiner.

JAMES W. LAWRENCE, RALPH G. NILSON,

Examiners.

S. ELBAUM, Assistant Examiner.

3. IN CARRYING OUT A NON-DESTRUCTIVE TEST BY IRRADIATING A MATERIAL TOBE TESTED WITH PENETRATING RADIATION; THE STEPS OF MASKING THE MATERIALTO BE TESTED BY A DEFORMABLE BAG-LIKE RECEPTABLE CONTAINING AN AQUEOUSMETAL IODIDE SOLUTION HAVING MASKING POWER FOR THE PENETRATING RADIATIONAPPROXMIATELY SIMILAR TO THAT OF THE MATERIAL TO BE TESTED, THE METALIODIDE BEING SELECTED FROM THE GROUP CONSISTING OF AQUEOUS SOLUTIONS OF:(A) ZINC IODIDE, (B) CADMIUM IODIDE, (C) IODIDES OF ZINC AND ALKALIMETAL, (D) IODIDES OF ZINC AND ALKALINE EARTH METAL, (E) IODIDES OFCADMIUM AND ALKALI METAL, AND (F) IODIDES OF CADMIUM AND ALKALINE EARTHMETAL.